This invention relates to an improvement of an air pressure shock absorber and more particularly to an absorber to absorb inner pressure in a chamber in order to stop a moving apparatus fixed to a piston when the piston passes through a predetermined stroke at the end of a cylinder or a housing.
In the field of mechanical air pressure shock absorbers, it is very difficult to smoothly stop a piston or a moving apparatus after sufficient absorption of energy of the moving apparatus, since air is used as a medium in the condition of a pressed fluid.
In the conventional air pressure shock absorber shown in FIG. 1 and FIG. 2, a piston 30 is slidably provided at an end of a rod 31 with a return spring means 20 in a housing or a cylinder 10. When external force F is added on an end of the rod 31, the piston 30 moves resistingly against the spring means 20 in the right direction as shown in FIG. 1, and air in a chamber 11 for the piston is gradually pressed and the energy of external force F is accumulated. As shown in FIG. 1, at another end of the housing, there are holes 42 and 52. A throttle valve means 40 is provided in the end portion of hole 42 and valve 41 of the throttle valve means 40 is also controllably provided in the hole 42. The hole 52 extends to small chamber 54 in which a check valve means 50 including a ball 51 and a spring 53 is installed, and the small chamber 54 communicates with a hole 55 and the ball 51 is provided contactably with an opening of the hole 55.
By this construction of the shock absorber, where the throttle valve means 40 is closed, internal pressure Pa in the chamber 11 for the piston increases greatly at an end portion of the stroke as shown by a curved line A in FIG. 2 showing the relationship between the stroke of the piston and pressure in FIG. 2. The increased pressure produces backlash or rebound as a bouding phenomenon by the force of counteraction against the piston 30, with a smooth stopping function achieved with difficulty.
From these problems in the shock absorber, the throttle valve means 40 was generally used to reduce internal pressure in the chamber 11 for a piston to obtain and use the curved line B in FIG. 2. In this case, it could reduce the force of counteraction at the near end of the stroke, but the energy of the external force being absorbed is reduced, with the absorber of this type being used only in a limited field. Also, when external force added to the rod is strong, even if the throttle valve means 40 is opened, the above stated bouding phenomenon occurs.